Obama spoke at the Lincoln Memorial last month during a 50th anniversary commemoration of the march, paying homage to unsung heroes of the civil rights movement, and was expected to deliver similar remarks Saturday night. First lady Michelle Obama, who was the keynote speaker last year, was accompanying the president.

Obama also is expected to highlight what the administration says are benefits for blacks and other minorities under his health care law, which he has said will make health care more affordable. The 3-year-old law has been contentious from the start, and on Friday, the Republican-controlled House approved another bill designed to wipe the law off the books, something that will not happen as long as Obama is president.

Obama has touted the law’s popular, consumer-friendly aspects, such as provisions requiring free mammograms and other health screenings or allowing dependent children to stay on their parents’ plans until age 26. He also has highlighted requirements for insurers to spend a certain percentage of premiums on health care.

Republicans argue that the law is making health care more, not less, expensive and is hurting the fragile economic recovery through mandates that are leading businesses to eliminate jobs or trim work hours.

Obama’s allies in organized labor are also now criticizing the law, fearing that it will jeopardize benefits for millions of union members.

Many people say they don’t understand the law. An NBC News/Wall Street Journal poll conducted earlier this month found just 30 percent of people saying they understand the law and how it will affect them. Sixty-nine percent said they understand the law only some or not very well.

Fewer than 4 in 10 people, or 31 percent, in the same poll said the law is a good idea, a low point since January 2010.

The Affordable Care Act requires everyone to have health insurance or face penalties. In less than two weeks, on Oct. 1, people without health coverage can begin signing up for subsidized private coverage through new state health insurance markets.